The present invention relates to a brake system for automotive vehicles, comprising a master cylinder, wheel cylinders and a device for anti-lock control. In the control mode for the positioning of at least one piston of the master cylinder in a desired position, a pump is provided, whose volume of delivery is variable, and which communicates by way of a hydraulic pressure line with the master cylinder and which positions the piston by the volume of fluid it delivers. The pump is part of a pump unit having at least one inlet line that provides a connection to the supply reservoir. An electronic control unit for the anti-lock control.
Anti-lock systems increasingly are used in the automotive vehicle industry. In certain applications of these anti-lock systems, hydraulic pumps are used for generating an auxiliary pressure in the control mode. Such anti-lock apparatus are known, for example, from German patent application P 37 31 603.6, corresponding to U.S. Pat. No. 4,826,255 which issued on May 2, 1989.
This patent application describes a brake system for automotive vehicles, comprising a master cylinder, wheel cylinders and a device for anti-lock control. For the positioning of the piston of the master cylinder in a desired position in the control mode, this brake system provides a pressure fluid source comprising a pump, whose volume of delivery is variable, which pump communicates by way of a hydraulic line with the master cylinder and which positions the piston by the volume of fluid it delivers.
In accordance with the objects of the present invention reliability and the desired pedal feeling are improved in such brake systems. More particularly, the "fail-safety" of the electric motor and thus of the pump driven by the electric motor as well as of the entire system are enhanced. Moreover, the brake pedal assumes a predefinable position in front of its initial position in the anti-lock control mode. It is desired that the electric motor continues its operation throughout the control mode. No repeated run-up should take place, thereby to avoid peaks in current. The relay stress is reduced, and the reliability of the entire system is increased.
The high starting currents of the electric motor for driving the pump will occur only once for each control action. The structural manufacturing effort and therefore expense is to be limited in order to obtain lower cost and in order to increase the reliability by relieving strain on the component parts. It is a further object to reduce the manufacturing cost of the overall brake system. The number of hydraulic lines, bores and valves is to be reduced.
In a brake system of dual-circuit design and including a tandem master cylinder, the following further object is to be achieved. In the event that only the push rod piston is sensed, then only the push rod piston is positioned by the pump volume of delivery, while the floating piston is slid back into its basic position, that is, the central-valve regulating position.